1. Field of the Invention
This invention pertains generally to the field of heat exchangers, and more particularly to devices for absorbing or emitting radiant heat energy in order to heat or cool specific objects. The invention finds particular application as a device for utilizing solar heat energy.
2. Description of the Prior Art
Conventional solar heat collectors generally contain a flat dark-colored panel or other means for absorbing the sun's radiation, and a system of pipes or channels for bringing a working fluid into thermal contact with this panel and carrying away the absorbed heat energy. The working fluid is distributed over the area of the panel through a series of "riser" tubes which are fed by, and discharge into, larger diameter "header" pipes, and these risers and headers together constitute the above-mentioned system. The header pipes are connected to a conduit for transporting the heated working fluid to the thermal "load", which may be an object desired to be heated or another heat exchanger, and seriately to a pump or other means for impelling the fluid through the system. The cooled working fluid is conducted back into the inlet header pipe of the collector, thereby completing the hydraulic circuit. The working fluid may be water or any other liquid substance with a substantial heat capacity. Water systems are commonly used to heat swimming pools, or to provide heated water for domestic or industrial use. A water-operated solar collector may also serve as a primary or auxiliary source of heat for space heating inside buildings.
In order to carry out the above heat exchange process with maximum thermal efficiency, it is desirable to reduce temperature gradients within the collector panel. Therefore the riser tubes should be relatively small in diameter and dispersed evenly over the collector panel, and the flow through the risers should be uniform in order to transport heat from each section of the collector panel with equal efficiency. This implies that the header pipes should discharge into or receive from each riser tube with an equal flow rate. If the risers intercommunicate with the headers through ordinary "tee" connections, this uniformity of flow may be difficult to accomplish in many circumstances without a complex and expensive mechanism for regulating simultaneously the flow through each riser tube. If the collector panel, riser tubes and header pipes are all perfectly horizontal, this uniformity may be achieved simply by constructing each riser tube to be the same diameter. However, in a tilted position, for example on a slanted roof, such a collector may produce a non-uniform flow rate as a result of gravitational effects on the fluid, with the concomitant appearance of "hot spots" in the panel and loss of efficiency. Similarly, varying the riser tube diameters to produce a uniform flow in a given slanted collector position may result in a non-uniform flow if the collector panel is placed in a different position. In short, it is difficult to obtain the desired uniformity of flow rate in conventional solar collector systems without unduly restricting the panel orientation.
A second problem with conventional collectors arises from the necessity for regular cleaning of the interior of the riser tubes. These tubes are small in diameter and subject to considerable heat, and deposits of dirt, rust, or other impurities develop on their interior walls. Such deposits constrict the flow through the risers and produce unevenness in the flow distribution, thereby decreasing the thermal and energetic efficiencies of the collector system. The riser tubes must be cleaned regularly to prevent buildup of these deposits. However, in a conventional collector these risers are terminated at both ends in header pipes or some other fluid distribution conduit system which does not allow ready and immediate access to the interior of the riser tubes for cleaning purposes. In order to clean the risers, they must either be removed from the collector or the hydraulic circuit must be broken open at some point, and this breaking point is generally different for each riser tube. Therefore cleaning the risers in a conventional collector presents a substantial plumbing task.
Conventional solar heat collectors are generally restricted in the panel shapes which may be allowed by the collector design. Many collectors are limited to rectangular or simple quadrangular configurations. In particular, where there are chimneys, ventilation pipes, or other obstacles on a roof, the conventional collectors must be built up in separate sections around these obstacles, thereby increasing substantially the complexity of the plumbing required to distribute the working fluid to these sections. If instead a hole is cut in the collector panel to accommodate the obstacle, the riser tube network must be designed to distribute the flow around this hole as uniformly as possible. Since the collector is often in a tilted position, this design task may not be a simple one, and in a conventional collector a given design will generally work only for certain panel orientations.
Therefore, it is an object of this invention to provide a solar heat collector system in which the working fluid is distributed evenly throughout the collector panel at a uniform flow rate in any panel position.
Another object of this invention is to provide a solar heat collector system which allows easy access to and cleaning of the interior walls of the working fluid distribution tubes, or "riser" tubes.
A further object of this invention is to provide a solar heat collector system which allows holes or indentations to be cut in the collector panel to accommodate obstacles without disturbance of the uniformity of flow rate of the working fluid in the remaining portions of the panel.